This invention relates to imaging systems, and more particularly, this invention relates to a system and method for identifying tie point collections for imagery.
The triangulation, i.e., the registration and control of satellite and aerial imagery, requires that the area of image overlap be correctly identified to ensure proper tie point collection. As is known, tie points are registered points of correspondence among various images, which can range in size and scale. For example, if an aircraft acquires images of a specific region at 5,500 feet, and then acquires images of the same region at 6,000 feet, the images will not be to scale and could differ as to cloud cover or other details.
Determining the areas of image overlap can be geographically challenging and time consuming if there are many image collections. This problem is further complicated when the tie points must be generated between stereo overlap areas.
In one prior art imaging technique, footprint polygons are used to identify the geographic extent of each individual image. A user, or the imaging processor, is then responsible for identifying the area of overlap. This task is easy for simple cases, but very difficult for complex overlap conditions.
FIG. 1 illustrates a simple image case where image footprint 1 and image footprint 2 have a single overlap 20. This area of overlap is not difficult to distinguish and process in most imaging systems. An intermediate, complex case is shown in FIG. 2 where image footprints 1-6 create two-way, three-way and four-way overlaps, as illustrated. This case is more difficult to process in many imaging systems.
One prior art imaging technique is disclosed in U.S. Pat. No. 5,808,626 to Givens et al. Tie points are selected within overlapping images, where the series of images are ordered to maximize the potential for successful phase correlation between adjacent images. Adjacent pairs in the ordered images are then phase correlated to determine translational offsets between adjacent pairs. The overlapping regions and adjacent pairs are assessed for normalized cross correlation and initial candidate tie points are selected within the regions at a reduced resolution. The initially selected tie points are then phase correlated at full resolution. Any surviving candidate tie point locations are further refined to sub-pixel accuracy.
This type of system provides an enhancement over many previous prior art techniques. It would be advantageous, however, if an image system""s potential to identify xe2x80x9cgoodxe2x80x9d locations for tie point collection could be implemented while offering building-by-building or feature-by-feature occlusion. It is also desirable if the use of imagery for overlap analysis could provide more accurate depiction of overlap areas as compared to four corner point polygons.
The present invention is advantageous and provides an enhanced system and method that identifies tie point collections used in imagery where overlaps can be readily understood. Imagery context can still be available with the system and method of the invention. Building-by-building or feature-by-feature occlusion is also possible. The use of imagery for overlap analysis in the present invention provides a more accurate depiction of overlap areas, as compared to processing and interpreting four corner point polygons. The present invention uses combiners to provide an easily understood depiction of the number of overlapping images/pairs at a discrete geographic location or region. These combiners preserve important features through the combination process, such as cloud coverage.
In accordance with the present invention, the system identifies tie point collections used in imagery and includes at least one image collection device for acquiring images of a selected region. A processor is operatively connected to the at least one image collection device. In one aspect of the invention, the at least one processor combines the acquired images into respective stereo images, such that only the stereo overlap remains. In another aspect of the present invention, the system can alone or in combination overlap combine the respective stereo images and color code the overlapped image areas based on the number of overlapping stereo images, to produce a colored overlay image and assist in triangulation and optimal texture selection.
In yet another aspect of the present invention, each area has a different number of overlapping stereo images that are color coded with a different color. Those areas having a closer number of overlapping stereo images are color coded with a similar shade of color. The maximum intensity amongst overlapping pixels as defined within the reference coordinate system can be passed through to form the stereo image. Pairs of images are combined into respective stereo images. The images can comprise satellite images and aerial photographs, as known to those skilled in the art.